For the purposes of this specification a shear damper means a cyclic shear energy absorber of the type described in WO94/13974; U.S. Pat. Nos. 4,117,637, 4,499,694; 4,593,502; and 4,713,917, the specifications of which are hereby incorporated by reference. Shear dampers have been used primarily in seismic isolation of structures. Seismic isolation involves increasing the natural period of a structure to outside the period of the exciting motion. This reduces the forces transmitted into a building through decoupling. The addition of a damping mechanism to dissipate the associated energy, thereby controlling the displacements and further reducing the accelerations transmitted to the structure, establishes a seismic protection system. This method of protection is suitable for structures with natural periods of less than 1.5 seconds. More of the principles of seismic isolation are described in Skinner et al, (see references at the end of the description).
Energy absorbers of this type to date have been designed to be weight bearing and are known in the art as lead rubber bearings. That is, the structure or parts of a structure to be damped from induced motion rest on top of the bearing and the bearings themselves rest either on the ground or on another part of the structure. These devices are intended to absorb earthquakes or wind loads, but are resistant to lesser forces.
It has been known for some time that energy absorbers can be used as dampers to control the elastic and plastic deformation of tall structures with natural periods greater than 1.5 seconds (Scawthorn et al, 1995). Dampers can be interposed laterally between structures or parts of structures to damp motion. The vibrations which may be damped may be very small.
It would be useful to be able to take advantage of shear dampers for uses other than as bearings in damping motion induced on structures. For example, shear dampers would be useful in applications such as damping vibrations in machinery, in penstocks of hydro-electric power stations or the like, in rolling stock such as heavy trucks or railway freight cars, carriages or engines or any similar vibrations.
It is an object of this invention to go some way towards achieving this desideratum or at least to offer the public a useful choice.